With the development of display technologies, flexible display devices have become more and more widely used. The flexible display device includes a flexible display panel, a touch screen, a polarizing layer, and a cover film disposed on a light-exiting side of the flexible display panel.
Due to its excellent bending, thermal, mechanical and optical properties, a colorless polyimide (PI) film can perfectly match flexible display characteristics, and is an ideal material for the cover film for the future flexible display technology.
However, polyimide films currently applied in industry for the cover film can still be observed with a slight yellow hue, which corresponds to a positive value of b* (b*=0.5˜0.8) in the CIE (Commission Internationale de L'Eclairage) LAB scale. Due to its own slight yellow hue, such a polyimide film may cause slight color distortion in the flexible display device after it is applied to a flexible display panel.